#include <iostream>
#include <vector>
#include <map>
using namespace std;

inline void read(int &x) {
    int s = 0, w = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9') {
        if (ch == '-') w = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9') {
        s = (s * 10) + ch - '0';
        ch = getchar();
    }
    x = s * w;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    
    int t = 0;
    int n;
    cin >> n;
    
    int val;
    for (int i = 0; i < 2*n-1; i++) {
        read(val);
        t = t ^ val;
    }
    cout << t << endl;
    return 0;
}

